You have a big, heavy truck. It takes large, powerful brakes to stop it. Also, if you were to put smaller brakes on it, you would still have to have custom rims made in the 6x135mm bolt pattern because no one makes on smaller than 17 inches. You would be cheaper, and much, much better off to stick with a 17 inch wheel/tire combo.
2005 Expy, 305/45-22 Falkens on 22x9.5 Eagle 026s.
2011 Jeep Wrangler Unlimited, 2" lift, 33" BFG AT KO's on 17x9 Eagle 197s.
2012 Ram 2500 crewcab diesel. 5" RCX lift, 355/60-20 Nitto Terra Grapplers on 20x9 KMC XD Spys.